The objective of the proposed research is to follow up on our interesting observation that copper absorption is enhanced in tumor bearing rats. This increase occurs in conjunction with other aberrations of copper metabolism in cancer, especially in elevated concentration and enhanced synthesis of the circulating copper protein, ceruloplasmin. Since so little is known about the basic mechanism of intestinal copper absorption and its regulation we will first study this process thoroughly in normal rats, and then make comparison with tumor bearing animals. The studies proposed involve in vivo and in vitro studies using 67Cu and 64Cu, following the uptake and distribution of copper within the mucosa, and its further transfer across the serosal surface. The influence of copper status and hormonal factors in the process of absorption will also be examined. It is expected that such studies will provide much basic information on the mechanism and regulation of copper absorption and explain the increased absorption which occurs in animals with tumors.